Each mini-MP3 digital sound module has full functions, including USB capabilities with SD card slot. We suggest using soothing music that nurtures and calms your little one to promote better feedings. Studies have found that nursery rhymes or classical music are excellent choices for the feeding experience. Each base unit which holds the sound module simply unscrew from the main body of the bottle. The unique design allows for safe and easy removal of the MP3 module during the cleaning process so it won't get wet, and fast assembly when done. Our products are parent approved and make for a happy, healthier baby.